watch event for die domain ?

watch event for die domain ?

[NAHieu]

Hi,

I am writing a small application to watch for xenstore events. I want
to know when a specific domain shutdown or reboot. It is best to watch
it via xenbus interface, but how? Is there any event or node can give
me such an event?

If not, I must periodically scan the domains (using libxc interface)
to detect if a domain dies, but that is not as good as xenbus
approach.

Many thanks.
Hieu

Re: watch event for die domain ?

[Christian Limpach]

On 9/10/05, NAHieu <nahieu@gmail.com> wrote:
> I am writing a small application to watch for xenstore events. I want
> to know when a specific domain shutdown or reboot. It is best to watch
> it via xenbus interface, but how? Is there any event or node can give
> me such an event?

You can have a watch on @releaseDomain, the watch will fire whenever
xenstored unmaps the store page it has mapped from the domain. 
There's also @introduceDomain for when xenstored maps the page after
the domain was created.

> If not, I must periodically scan the domains (using libxc interface)
> to detect if a domain dies, but that is not as good as xenbus
> approach.

Yeah, polling is definitely not the way to go ;-)

     christian

Re: watch event for die domain ?

[Rusty Russell]

On Sun, 2005-09-11 at 00:53 +0100, Christian Limpach wrote:
> On 9/10/05, NAHieu <nahieu@gmail.com> wrote:
> > I am writing a small application to watch for xenstore events. I want
> > to know when a specific domain shutdown or reboot. It is best to watch
> > it via xenbus interface, but how? Is there any event or node can give
> > me such an event?
> 
> You can have a watch on @releaseDomain, the watch will fire whenever
> xenstored unmaps the store page it has mapped from the domain. 
> There's also @introduceDomain for when xenstored maps the page after
> the domain was created.

Speaking of which, I have a patch which changes over introduce/release
to a write/rm in /tool/xenstored/domain/<id>, so this will combine
nicely, too.  (Part of the patch series to make xenstored restartable).

This is probably more generically useful, and avoids turning xenstored
into an event mechanism 8)

Cheers,
Rusty.
-- 
A bad analogy is like a leaky screwdriver -- Richard Braakman